140 Managing a Switch StackHow is the Firmware Updated on the Stack?When you add a new switch to a stack, the Stack Firmware Synchronizationfeature automatically synchronizes the firmware version with the versionrunning on the stack master. The synchronization operation may result ineither upgrade or downgrade of firmware on the mismatched stack member.Upgrading the firmware on a stack of switches is the same as upgrading thefirmware on a single switch. After you download a new image by using the FileDownload page or copy command, the downloaded image is distributed to allthe connected units of the stack. For more information about downloadingand installing images, see "Managing Images and Files " on page 349.What is Stacking Standby?A Standby unit is preconfigured in the stack. If the current Master unit fails,the Standby unit becomes the Master unit. If no switch is pre-configured asthe Standby unit, the software automatically selects a Standby unit from theexisting stack units.When the failed Master resumes normal operation, it joins the stack as amember (not a Master) if the new Master unit has already been elected.The Master unit copies its running configuration to the Standby unitwhenever it changes (subject to some restrictions to reduce overhead). Thisenables the Standby unit to take over the stack operation with minimalinterruption if the Master unit becomes unavailable.The running-config synchronization also occurs:• when you save the running configuration to the startup configuration onthe Master unit.• when the backup unit changes.What is Nonstop Forwarding?Networking devices, such as the PowerConnect 7000 Series switches, areoften described in terms of three semi-independent functions called theforwarding plane, the control plane, and the management plane. Theforwarding plane forwards data packets and is implemented in hardware. Thecontrol plane is the set of protocols that determine how the forwarding planeshould forward packets, deciding which data packets are allowed to beforwarded and where they should go. Application software on the
